Generating performance of a tubular permanent magnet linear generator for application on free-piston engine generator prototype with wide-ranging operating parameters

This paper proposes a tubular permanent magnet linear generator (TPMLG) applied to the free-piston engine generator and establishes a test rig of the TPMLG. A large amount of experimental data was obtained under unfired conditions and a 2D finite element model of the TPMLG was developed and validated. Then, the electromagnetic characteristics were analyzed under no-load and load conditions. The effects of motion profile, operating frequency, velocity, stroke length, oscillation center position and load resistance on the output performance and generating efficiency (η) of TPMLG were investigated. Results show that the phase angle and distortion rate of the output voltage and current will vary under different motion profiles. As the operating frequency, velocity and stroke length increase, the output voltage, current, power and loss power increase gradually, while η increases at first and subsequently plateaus. When peak velocity is fixed and stroke length increases, both output power and copper loss rapidly increase and then remain steady. Meanwhile, there is only a slight change in generating efficiency. There is an optimal load resistance of approximately 6 Ω needed to achieve maximum output power. When load resistance is greater than 40 Ω, changes in load voltage, current and η become insignificant and the η reaches a maximum of 92.54%. Furthermore, the OCP changes the load voltage and current curves but has little effect on output power in terms of the RMS value.